Cryogenic mechanical loss of amorphous germania and titania-doped germania thin films

Abstract The mechanical loss of amorphous thin films of germania (GeO 2 ) and titania-doped germania (Ti:GeO 2 ) deposited by ion-beam sputtering onto silicon double-paddle oscillators was studied from 10 K to 290 K. Undoped germania was found to show a wide cryogenic mechanical loss peak centered at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>60</mml:mn> </mml:math> K with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ϕ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3.1</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> , which decreases to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.1</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> as Ti-concentration increases to 44%. In addition to decreasing the height of this low-temperature peak, Ti-doping increases its width, and shifts its position toward lower temperatures. Annealing reduces the room temperature mechanical loss of Ti:GeO 2 and increases its cryogenic mechanical loss, which is consistent with trends observed in most amorphous oxides.